the Primary Rocks and the Oolitic Series in the North of Scotland. 157 



appears to be unconformable to the lias, and on the west coast of the same 

 county. They are unconformable to the newer red sandstone of Loch Groi- 

 nard, and to the lias of Applecross. In regard to the great central deposit of 

 Caithness schist,, we are not able to identify it with any part of the English 

 series which has hith&rto been described. It is of great thickness, — is void of 

 shells or corals, — exhibits a very few obscure vegetable impressions, — but con- 

 tains from the highest down to the lowest beds a great number of fish of two 

 new genera, as well as a species of Trionyx (?), probably all of fresh-water 

 origin. Considered as a whole, it has a much older character than the mag- 

 nesian limestone series ; and the bottom beds alternate with the old conglo- 

 merates, and cannot, therefore, be entirely separated from them. Moreover, 

 the fish are not of the same species with any which have yet been dis- 

 covered, either in the marl-slate of Durham, or in the copper-slate of Ger- 

 many. We are, for these reasons, unwilling to consider the Caithness schist 

 as the equivalent of the Thuringerwald marl-slate. It appears to be nearly 

 of the same age with the carboniferous order, and the conjecture is fortified 

 by the mineralogical characters of the middle deposit on the shores of the 

 Murray Firth. The calcareo-bituminous strata are there subordinate to 

 sandstone, many beds of which are perfectly analogous to the white and 

 reddish sandstones which form the greatest part of the carboniferous group 

 in the Isle of Arran. 



Pursuing the analogies presented by the Arran section, we were led to con- 

 clude that the upper red sandstone of Dunnet Head, and of the opposite cliffs 

 of the Orkneys, was the representative of the lowest division of the new red 

 sandstone group, to which in position it seems to approximate; but its mine- 

 ralogical character is not decisive ; and with the exception of Loch Groinard, 

 the upper or new red conglomerates do not appear in any part of the coast we 

 have examined. Again, there is a break in the continuity of the secondary 

 deposits above described ; for there is no single section which conducts, unin- 

 terruptedly, from the old conglomerates to the lias, and the equivalent of the 

 oolites. We believe it to be impossible to determine where the interruption 

 of continuity takes place. 



The exact relations of the upper red sandstone of the Pentland Firth must, 

 therefore, remain in some degree of doubt. In external character, it perhaps 

 most nearly resembles that system of red sandstone beds which, in the Isle of 

 Arran, are interposed between the true carboniferous strata and the upper red 

 conglomerates. 



As a general result of the previous details, it follows that the enormous 

 masses of red sandstone and conglomerate on the coasts of the Highlands are. 



